Seal assembly with secondary retention feature

ABSTRACT

An assembly for a gas turbine engine according to an example of the present disclosure includes, among other things, a gas turbine engine component that has a first interface portion, and a support that has a mounting portion and a second interface portion, the mounting portion attachable to an engine static structure, a first retention feature that releasably secures the first interface portion to the support in a first installed position of the gas turbine engine component, and a second retention feature dimensioned to secure the first interface portion to the second interface portion in a second installed position of the gas turbine engine component. The first installed position differs from the second installed position, and one of first and second retention features is dimensioned to carry the gas turbine engine component in response to release of another one of the first and second retention features. A method of sealing for a gas turbine engine is also disclosed.

BACKGROUND

This disclosure relates to positioning of components of a gas turbineengine.

Gas turbine engines can include a fan for propulsion air and to coolcomponents. The fan also delivers air into a core engine where it iscompressed. The compressed air is then delivered into a combustionsection, where it is mixed with fuel and ignited. The combustion gasexpands downstream over and drives turbine blades. Static vanes arepositioned adjacent to the turbine blades to control the flow of theproducts of combustion.

The turbine section may include multiple stages of rotatable blades andstatic vanes. An annular shroud or blade outer air seal may be providedaround the blades in close radial proximity to the tips of the blades toreduce the amount of gas flow that escapes around the blades. The shroudtypically includes a plurality of arc segments that arecircumferentially arranged about the blades.

SUMMARY

An assembly for a gas turbine engine according to an example of thepresent disclosure includes a gas turbine engine component that has afirst interface portion, and a support that has a mounting portion and asecond interface portion, the mounting portion attachable to an enginestatic structure, a first retention feature that releasably secures thefirst interface portion to the support in a first installed position ofthe gas turbine engine component, and a second retention featuredimensioned to secure the first interface portion to the secondinterface portion in a second installed position of the gas turbineengine component. The first installed position differs from the secondinstalled position, and one of first and second retention features isdimensioned to carry the gas turbine engine component in response torelease of another one of the first and second retention features.

In a further embodiment of any of the foregoing embodiments, the secondretention feature includes an interface flange extending outwardly fromthe first interface portion and includes a support flange extending fromthe second interface portion. The interface flange is dimensioned to siton the support flange in the second installed position.

In a further embodiment of any of the foregoing embodiments, the gasturbine engine component is a seal arc segment including a sealingportion dimensioned to bound a gas path surface. The first interfaceportion includes an interface bore. The first retention feature includesa retention pin slidably received in the interface bore to secure thefirst interface portion to the support in the first installed positionof the seal arc segment, and the interface bore is dimensioned such thatthe seal arc segment sits on an outer periphery of the retention pin inthe first installed position.

In a further embodiment of any of the foregoing embodiments, the secondretention feature includes an interface flange extending outwardly fromthe first interface portion and includes a support flange extending fromthe second interface portion. The interface flange is dimensioned to siton the support flange in the second installed position.

In a further embodiment of any of the foregoing embodiments, the secondinterface portion includes a support bore dimensioned to at leastpartially receive the retention pin to establish the first installedposition of the seal arc segment.

In a further embodiment of any of the foregoing embodiments, theinterface bore is dimensioned such that the seal arc segment sits on anouter periphery of the retention pin in the first installed position.

In a further embodiment of any of the foregoing embodiments, theinterface flange of the seal arc segment comprises a ceramic material.

In a further embodiment of any of the foregoing embodiments, theinterface flange includes a sacrificial member dimensioned to engage thesupport flange in the second installed position.

In a further embodiment of any of the foregoing embodiments, the gasturbine engine component is a seal arc segment including a sealingportion dimensioned to bound a gas path surface, and the sealing portionand the first interface portion of the seal arc segment comprise aceramic material.

In a further embodiment of any of the foregoing embodiments, the gasturbine engine component is a seal arc segment including a sealingportion dimensioned to bound a gas path surface, and further including aseal plate attachable to the support, and a seal member captured betweenthe seal arc segment and the seal plate. The first interface portionincludes a first flange. The seal plate includes a plate flange, and theplate flange is dimensioned to carry the seal arc segment in the secondinstalled position.

In a further embodiment of any of the foregoing embodiments, the firstinterface portion includes an interface bore. The first retentionfeature includes a retention pin slidably received in the interface boreto secure the first interface portion to the support in the firstinstalled position of the seal arc segment, and the seal plate includesa plate bore dimensioned to at least partially receive the retention pinto establish the first installed position of the seal arc segment.

A gas turbine engine according to an example of the present disclosureincludes an engine case extending along an engine longitudinal axis, anarray of blades rotatable about the engine longitudinal axis, and a sealassembly including an array of blade outer air seals (BOAS) arrangedabout the array of blades. Each of the BOAS has a sealing portion and afirst interface portion. The sealing portion is dimensioned to bound acore flow path, and the first interface portion including at least oneinterface bore. At least one support is attached to the engine case. Afirst retention feature has a plurality of retention pins dimensioned toengage the at least one support and the first interface portion of arespective one of the BOAS such that the BOAS are carried by theretention pins in a first installed position. A second retention featureis dimensioned to bound radial movement of the BOAS towards the enginelongitudinal axis in a second installed position of the BOAS.

In a further embodiment of any of the foregoing embodiments, each of theBOAS comprises a ceramic material.

In a further embodiment of any of the foregoing embodiments, each of theretention pins is slidably received in a respective interface bore ofthe first interface portion and at least partially received in arespective support bore of the at least one support such that the firstinterface portion sits on a radially outer surface of the respectiveretention pin in the first installed position.

In a further embodiment of any of the foregoing embodiments, the sealassembly includes a seal plate releasably secured to the at least onesupport, and each of the retention pins is inserted into a respectiveplate bore of the seal plate to establish the first installed position.

In a further embodiment of any of the foregoing embodiments, a firstretention hook of the first interface portion is dimensioned to sit on asecond retention hook of the at least one support in the secondinstalled position.

A method of sealing for a gas turbine engine according to an example ofthe present disclosure includes positioning a first interface portion ofa seal arc segment relative to a second interface portion of a supportsuch that engagement of the first and second interface portionsestablishes a first installed position of the seal arc segment in whichthe seal arc segment is carried by the support, and inserting aretention pin in an interface bore of the seal arc segment and a supportbore of the support such that engagement of the retention pin withsurfaces of the interface bore and surfaces of the support boreestablishes a second installed position of the seal arc segment in whichthe seal arc segment is carried by the retention pin. One of the firstand second installed positions is established in response to release ofthe seal arc segment from another one of the first and second installedpositions subsequent to the positioning and inserting steps.

In a further embodiment of any of the foregoing embodiments, the sealarc segment comprises a ceramic material.

A further embodiment of any of the foregoing embodiments includessecuring a seal plate to the support, and inserting the retention pin ina plate bore of the seal plate to establish the second installedposition.

In a further embodiment of any of the foregoing embodiments, the firstinterface portion includes a first flange. The second interface portionincludes a second flange, and the first flange is dimensioned to sit onthe second flange in the first installed position.

The various features and advantages of this disclosure will becomeapparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example gas turbine engine.

FIG. 2 illustrates an axial view of an example blade outer air sealassembly including a plurality of seal arc segments.

FIG. 3 illustrates a section view of the seal assembly taken along line3-3 of FIG. 2 including a representative one of the seal arc segments ina first installed position.

FIG. 4 illustrates a perspective view of the seal arc segment of FIG. 3.

FIG. 5 illustrates a section view of the seal arc segment of FIG. 3 in asecond installed position.

FIG. 6 illustrates a section view of a seal assembly according toanother example.

FIG. 7A illustrates an example retention pin having a circular profile.

FIG. 7B illustrates an example retention pin having an ellipticalprofile.

FIG. 7C illustrates an example retention pin having a triangularprofile.

FIG. 8 illustrates a seal assembly according to another example.

FIG. 9 illustrates a seal assembly according to yet another example.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. The fan section 22 drivesair along a bypass flow path B in a bypass duct defined within a housing15 such as a fan case or nacelle, and also drives air along a core flowpath C for compression and communication into the combustor section 26then expansion through the turbine section 28. Although depicted as atwo-spool turbofan gas turbine engine in the disclosed non-limitingembodiment, it should be understood that the concepts described hereinare not limited to use with two-spool turbofans as the teachings may beapplied to other types of turbine engines including three-spoolarchitectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects, a first (or low) pressure compressor 44 and a first (orlow) pressure turbine 46. The inner shaft 40 is connected to the fan 42through a speed change mechanism, which in exemplary gas turbine engine20 is illustrated as a geared architecture 48 to drive a fan 42 at alower speed than the low speed spool 30. The high speed spool 32includes an outer shaft 50 that interconnects a second (or high)pressure compressor 52 and a second (or high) pressure turbine 54. Acombustor 56 is arranged in exemplary gas turbine 20 between the highpressure compressor 52 and the high pressure turbine 54. A mid-turbineframe 57 of the engine static structure 36 may be arranged generallybetween the high pressure turbine 54 and the low pressure turbine 46.The mid-turbine frame 57 further supports bearing systems 38 in theturbine section 28. The inner shaft 40 and the outer shaft 50 areconcentric and rotate via bearing systems 38 about the engine centrallongitudinal axis A which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path C. The turbines 46, 54 rotationally drivethe respective low speed spool 30 and high speed spool 32 in response tothe expansion. It will be appreciated that each of the positions of thefan section 22, compressor section 24, combustor section 26, turbinesection 28, and fan drive gear system 48 may be varied. For example,gear system 48 may be located aft of the low pressure compressor, or aftof the combustor section 26 or even aft of turbine section 28, and fan42 may be positioned forward or aft of the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five 5:1. Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1 and less than about 5:1. Itshould be understood, however, that the above parameters are onlyexemplary of one embodiment of a geared architecture engine and that thepresent invention is applicable to other gas turbine engines includingdirect drive turbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and35,000 ft (10,668 meters), with the engine at its best fuelconsumption—also known as “bucket cruise Thrust Specific FuelConsumption (‘TSFC’)”—is the industry standard parameter of 1 bm of fuelbeing burned divided by 1 bf of thrust the engine produces at thatminimum point. “Low fan pressure ratio” is the pressure ratio across thefan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The lowfan pressure ratio as disclosed herein according to one non-limitingembodiment is less than about 1.45. “Low corrected fan tip speed” is theactual fan tip speed in ft/sec divided by an industry standardtemperature correction of [(Tram ° R)/(518.7° R)]^(0.5). The “Lowcorrected fan tip speed” as disclosed herein according to onenon-limiting embodiment is less than about 1150 ft/second (350.5meters/second).

FIG. 2 illustrates an axial view of an example assembly 60 for a gasturbine engine. The assembly 60 can be incorporated into a portion ofthe engine 20 of FIG. 1, such as the turbine section 28. In theillustrative example of FIG. 2, the assembly 60 is a blade outer airseal assembly for sealing portions of a gas turbine engine. The assembly60 can alternatively or additionally be adapted for other portions ofthe engine 20, such as an upstream stage of the compressor section 24 orcombustor panels defining portions of a combustion chamber located inthe combustor section 26. Although the teachings herein primarily referto a two-spool gas turbine engine having a fan, other systems canbenefit from the teachings herein, such as engines without a fan andother ground based systems.

The assembly 60 is positioned radially outward of a rotor 62 having anarray (or row) of airfoils or rotatable blades 64. The blades 64 arerotatable about the engine longitudinal axis A in a gas path GP, such asthe core flow path C (FIG. 1). The blades 64 are positioned adjacent toone or more rows of vanes 65 (one shown in FIG. 3 for illustrativepurposes). Each vane 65 can be dimensioned to direct flow in the gaspath GP towards the blades 64.

The assembly 60 includes one or more gas turbine engine components 66.In the illustrative example of FIG. 2, the components 66 are blade outerair seals (BOAS) or seal arc segments. In the illustrative example ofFIG. 2, the assembly 60 includes an array of seal arc segments 66circumferentially arranged in an annulus around the engine longitudinalaxis A and about the blades 64. The seal arc segments 66 are mounted toat least one support 68, which can be continuous or can be segmented asa plurality of supports (illustrated by dashed lines in FIG. 2). Thesupport 68 is mounted or attached to an engine case 70 through one ormore connections 69. The engine case 70 is arranged about and extendsalong the engine axis A. In other examples, the seal arc segments 66 aredirectly attached to the engine case 70. The engine case 70 can bemounted or attached to, or form a portion of, the engine staticstructure 36 (see also FIG. 1).

Each seal arc segment 66 can be formed of a material having a hightemperature capability. Example high temperature materials includemetallic alloys and ceramic-based materials, such as a monolithicceramic or a ceramic matrix composite (CMC) material. An example of ahigh temperature metallic alloy is a nickel-based alloy. Monolithicceramics include, but are not limited to, silicon carbide (SiC) orsilicon nitride (Si₃N₄). In other examples, each seal arc segment 66 isformed of high-toughness material such as, but not limited to, singlecrystal metallic alloys.

The seal arc segments 66 are positioned in close radial proximity totips 64T of the blades 64 to reduce the amount of gas flow that escapesaround the blades 64 and through a clearance gap G. The engine 20 caninclude an active or passive clearance control system to adjust theclearance gap G to a desired dimension during one or more operatingconditions of the engine 20. The clearance gap G may also vary duringoperation of the engine 20, such as between a non-operating, cold statecondition, and an operating condition such as a cruise and/or takeoffcondition of the engine 20.

Referring to FIG. 3, with continued reference to FIG. 2, an axial crosssection view of the assembly 60 is shown. FIG. 4 illustrates aperspective view of an example seal arc segment 66. Each seal arcsegment 66 includes a sealing portion 72 and a first interface portion74. The sealing portion 72 includes a generally arcuate sealing surface(or face) 72A extending between circumferential mate faces 72B, asillustrated by FIG. 4 (see also FIG. 2). The sealing surface 72A isdimensioned to bound portions of the gas path GP, such as the core flowpath C of FIG. 1. The sealing portion 72 and first interface portion 74can be made of any of the materials disclosed herein, including aceramic-based material.

The first interface portion 74 of the seal arc segment 66 includes apair of rails 74R (indicated at 74R-1, 74R-2) extending radiallyoutwardly from the sealing portion 72. An elongated slot or backsidecavity 74S extends between the rails 74R. In examples, cooling airflowis communicated to the backside cavity 74S to cool adjacent portions ofthe seal arc segment 66.

The first interface portion 74 can include a pair of interface flanges74F (indicated at 74F-1, 74F-2) extending outwardly from the respectiverails 74R-1, 74R-2 of the first interface portion 74. The interfaceflanges 74F and rails 74R can be made of any of the materials disclosedherein, including a ceramic-based material.

The support 68 includes a mounting portion 76 and a second interfaceportion 78, which can be made of a metallic material. The mountingportion 76 is attachable to the engine static structure 36 directly orthrough the engine case 70.

The assembly 60 includes a first (e.g., primary) retention feature 80and a second (e.g., secondary) retention feature 82 that mount the sealarc segments 66 to the support 68 during engine operation. One of thefirst and second retention features 80, 82 is dimensioned to carry theseal arc segment 66 in response to release of another one of the firstand second retention features 80, 82. For the purposes of thisdisclosure, the term “primary” retention feature refers to anarrangement that at least initially bears a load of the seal arc segmentin an installed position, and the term “secondary” retention featurerefers to an arrangement that does not bear any load or bearssubstantially less of the load of the seal arc segment when the load isborne by the primary retention feature in the installed position.Although the first and second retention features 80, 82 are primarilyreferred to as primary and secondary retention features, respectively,in the example of FIGS. 3-5, in other examples the first retentionfeature 80 serves as the secondary retention feature, and the secondretention feature 82 serves as the primary retention feature. Theretention features 80, 82 are dimensioned to establish and maintain aset of predetermined distances between the sealing surface 72A of theseal arc segments 66 and the blade tips 64T across the clearance gap GP.The first and second retention features 80, 82 can be dimensioned withrespect to expected manufacturing and design tolerances and expectedthermal distortions of the components of the assembly 60 during engineoperation.

In some scenarios, a position of the first interface portion 74 changesrelative to the second interface portion 78 due to a release of thefirst retention feature 80 when the seal arc segment 66 is situated inthe first installed position. Such changes may occur due to shearing ofa retention pin 84, or delamination or sheering of the CMC material ofthe seal arc segment 66 due to stress concentrations when the seal arcsegment 66 is situated in the first installed position, for example. Thefirst and second retention features 80, 82 cooperate to maintain aclearance between the seal arc segments 66 and the adjacent blades 64.

Various first and second retention features 80, 82 can be utilized. Thefirst and second retention features 80, 82 can be the same or candiffer. The first retention feature 80 can be arranged to releasablysecure the first interface portion 74 to the support 68 in a firstinstalled position of the seal arc segment 66. Example retentionfeatures include fasteners such as clips, pins, bolts and rivets, aswell as other components that mechanically join objects together such asa length of wire. In the illustrative example of FIGS. 3-4, the firstretention feature 80 includes one or more retention pins (or members) 84dimensioned to engage the support 68 and the first interface portion 74of a respective one of the seal arc segments 66 such that each of theseal arc segments 66 is carried by one or more of the retention pins 84in the first installed position of the seal arc segment 66. The seal arcsegment 66, support 68 and retention pins 84 are separate and distinctcomponents.

Each retention pin 84 includes an elongated main body 84A extendingbetween opposed first and second end portions 84B, 84C. The firstinterface portion 74 includes one or more interface bores 74B extendingthrough a respective rail 74R. Each interface bore 74B of the rail 74R-1is partially or completely radially aligned with a respective interfacebore 74B of the rail 74R-2. Each interface bore 74B has a diameter thatis greater than a diameter of a respective one of the retention pins 84.The second interface portion 78 includes one or more support bores 78B(one shown in FIG. 3 for illustrative purposes). The interface andsupport bores 74B, 78B are dimensioned to at least partially receive arespective retention pin 84 to establish the first installed position ofthe seal arc segment 66.

The assembly 60 includes a seal plate 86 attached or releasably securedto the support 68. Various techniques can be utilized to secure the sealplate 86 to the support 68, such as one or more fasteners. The sealplate 86 has a generally arcuate geometry and extends about the enginelongitudinal axis A (shown in dashed lines in FIG. 2 for illustrativepurposes). The seal plate 86 includes a plate flange 86F extendingoutwardly from a plate body 86A. The seal plate 86 includes one or moreplate bores 86B (one shown in FIG. 3 for illustrative purposes)dimensioned to at least partially receive the retention pin 84 toestablish the first installed position of the seal arc segment 66.

A seal member 87 is captured between the seal arc segment 66 and sealplate 86. In the illustrative example of FIG. 3, the seal member 87 is aW-seal arranged to oppose flow along an axial gap between the seal arcsegment 66 and seal plate 86.

Each of the interface flanges 74F can include a sacrificial member 88disposed on surfaces of the flange 74F. The sacrificial member 88 can bemade of a material that differs from a material of the respective flange74F. The sacrificial member 88 can be machined or otherwise formed tohave a complementary geometry with the respective flange 78F/86F whilepreserving a construction of the underlying laminate structure. Thesacrificial member 88 can be a coating or constructed from one or moresacrificial plies or layers, and is dimensioned to eliminate orotherwise reduce direct contact between surfaces of the interface flange74F and the respective flange 78F/86F. An example coating includes asilicon metal that is adapted to substantially match a rate of thermalexpansion of the seal arc segment 66 to reduce a likelihood of spallingof the laminate structure of the CMC layup.

The support 68 can include at least one face seal 90 dimensioned toengage the first interface portion 74 directly or along the adjacentsacrificial member 88. The face seal 90 is dimensioned to oppose flowalong an axial gap between the first interface portion 74 and secondinterface portion 78 of the support 68.

In the first installed position, each interface bore 74B is partially orcompletely radially aligned with an adjacent support bore 78B and/orplate bore 86B. Each retention pin 84 is slidably received in, andextends at least partially through, the interface bore 74B of each rail74R-1, 74R-2 and is received in a respective support bore 78B and platebore 86B to secure the first interface portion 74 to the support 68 inthe first installed position.

The support 68 and seal plate 86 are dimensioned to trap the retentionpin(s) 84 in the first installed position. The first end portion 84B ofthe retention pin 84 is at least partially inserted into the respectivesupport bore 78B, and the second end portion 84C of the retention pin 84is at least partially inserted into the respective plate bore 86B.Various techniques can be utilized to secure the retention pin 84 to thesupport 68 and/or seal plate 86, such as press fitting or threadedlyattaching the retention pin 84 in the support bore 78B and/or plate bore86B.

Each interface bore 74B is dimensioned such the rails 74R of the sealarc segment 66 are carried by an outer periphery 84D of the retentionpin(s) 84 in the first installed position. The interface bores 74B aredimensioned such that the rails 74R of the first interface portion 74sit on a radially outer surface 84R0 of the retention pin 84 in thefirst installed position, as illustrated by FIG. 3. The interface bores74B is dimensioned such that the rails 74R are spaced apart from aradially inner surface 84RI of the retention pin 84 in the firstinstalled position to accommodate differences in thermal expansion ofrails 74R, retention pin 84, support 68 and/or support plate 86 duringengine operation. In other examples, a diameter of the retention pin 84is substantially equal to a diameter of the interface bores 74B.

The second retention feature 82 is dimensioned to secure the firstinterface portion 74 of the seal arc segment 66 to the second interfaceportion 78 of the support 68 in a second installed position of the sealarc segment 66, as illustrated by seal arc segment 66′ of FIG. 5. Thefirst installed position of the seal arc segment 66 differs from thesecond installed position of seal arc segment 66′.

The second retention feature 82 is dimensioned to bound radial movementof the seal arc segment 66 towards the engine longitudinal axis A andsecure the seal arc segment 66 in the second installed position inresponse to a release of the first retention feature 80 when the sealarc segment 66 is in the first installed position. The second retentionfeature 82 is dimensioned such that a clearance gap G′ is maintainedbetween a sealing surface 72A′ of the seal arc segment 66′ and a bladetip 64T′ of the adjacent blade 64′. In examples, the first installedposition of the seal arc segment 66 is radially outward of the secondinstalled position of the seal arc segment 66′ such that a dimension ofthe clearance gap G is greater than a dimension of the clearance gap G′.

In the illustrative example of FIG. 3, the support 68 includes a supportflange 78F extending outwardly from the second interface portion 78. Theinterface flanges 74F are at least partially axially aligned with therespective the support flange 78F and plate flange 86F relative to theengine longitudinal axis A. The interface flange(s) 74F together withthe support flange 78F and/or plate flange 86F cooperate to establishthe second retention feature 82. The support flange 78F and/or plateflange 86F are dimensioned to carry a load of the seal arc segment 66 inthe second installed position, but not in the first installed position,in response to a release of the first retention feature 80 when the sealarc segment 66 is situated in the first installed position. The secondretention feature 82 can be dimensioned to carry at least a portion orsubstantially all of the load of the seal arc segment 66.

In the illustrative examples of FIG. 5, the interface flange(s) 74F′ aredimensioned to sit on the support flange 78F′ and plate flange 86F′ inthe second installed position to limit radially inward movement of theseal arc segment 66′ towards the engine longitudinal axis A. Eachsacrificial member 88′ is dimensioned to engage the support flange 78F′and/or plate flange 86F′ in the second installed position. In otherexamples, the sacrificial member 88′ is disposed on the support flange78F′ and/or plate flange 86F′ or is omitted such that the interfaceflanges 74F′ directly contacts the support flange 78F′.

The assembly 60 can be assembled as follows. The first interface portion74 of the seal arc segment 66 is positioned relative to the secondinterface portion 78 of the support 68 such that engagement of the firstand second interface portions 74, 78 establishes the second installedposition of the seal arc segment 66 in which the seal arc segment 66 iscarried by the support 68. At least one retention pin 84 is moved in adirection D2 (FIGS. 3-4) and is inserted in the interface bore(s) 74Band in the support bore 78B such that engagement of the retention pin 84with surfaces of the interface bore(s) 74B and surfaces of the supportbore 78B establishes the first installed position in which the seal arcsegment 66 is carried by the retention pin 84. Thereafter, the sealplate 86 is secured to the support 68 to trap the retention pins 84 andto establish the first installed position. The retention pin 84 isreceived in a respective plate bore 86F.

During operation, each seal arc segment 66 is carried by the firstretention feature 80 in the first installed position to seal portions ofthe gas path GP. Upon release of the first retention feature 80, theseal arc segment 66 moves in the radially inward direction D1 (FIG. 5)towards the engine longitudinal axis A from the first installed positionto the second installed position. The second retention feature 82captures the seal arc segment in the second installed position to reducea likelihood of contact between the seal arc segment 66 and adjacentblades 64 during operation. The second retention feature 82 can beadapted to redistribute pressure loads carried by the first retentionfeature 80 over additional surface area due to engagement of the firstand second retention features 80, 82 in the second installed position ofthe seal arc segment 66.

FIG. 6 illustrates an assembly 160 for a gas turbine engine according toanother example. In this disclosure, like reference numerals designatelike elements where appropriate and reference numerals with the additionof one-hundred or multiples thereof designate modified elements that areunderstood to incorporate the same features and benefits of thecorresponding original elements. The assembly 160 includes at least oneseal arc segment 166, at least one support 168 and a seal plate 186. Theseal arc segment 166 and support 168 cooperate to establish a firstretention feature 180 and a second retention feature 182.

The seal arc segment 166 includes a first interface portion 174extending outwardly from a sealing portion 172. The first interfaceportion 174 includes a pair of rails 174R (indicated at 174R-1, 174R-2).A pair of retention hooks 174H (indicated at 174H-1, 174H-2) extendtransversely from the respective rails 174R-1, 174R-2.

The support 168 includes a second interface portion 178 having a pair ofretention hooks 178H (indicated at 178H-1, 178H-2) dimensioned to matewith the retention hooks 174H-1, 174H-2. A sacrificial member 188 can bedisposed on surfaces of each retention hook 174H and can be dimensionedto engage surfaces of the adjacent retention rail 178H.

The retention hooks 174H, 178H cooperate to establish the firstretention feature 180. The retention hooks 174H of the seal arc segment166 are dimensioned to sit on and be carried by the retention hooks 178Hof the support 168 in a first (e.g., primary) installed position of theseal arc segment 166.

The second retention feature 182 includes one or more retentions pin 184that engages the second interface portion 178 to secure the seal arcsegment 166 to the support 168. In the illustrative example of FIG. 6,the second retention feature 182 a pair of retention pins 184 (indicatedat 184-1, 184-2) that mount the seal arc segment 166 to the support 168.Each retention pin 184 is slidably received in, and extends at leastpartially through, an interface bore 174B of the respective rail 174Rand is inserted in a respective support bore 178B to secure the firstinterface portion 174 to the support 168 in a second (e.g., secondary)installed position of the seal arc segment 166. Each interface bore 174Bis dimensioned such that the rails 174R sit on and are carried by theretention pins 184 in the second installed position, but not in thefirst installed position, in response to movement of the seal arcsegment 166 in a radially inward (or first) direction D1 towards theengine longitudinal axis A from the first installed position to thesecond installed position. The second installed position of the seal arcsegment 166 is illustrated by dashed line 166′ in FIG. 6.

The retention pins can have various profiles, such as a circular crosssection as illustrated by retention pin 284 of FIG. 7A, a non-circularelliptical cross section as illustrated by retention pin 384 of FIG. 7B,or a generally triangular cross section as illustrated by retention pin484 of FIG. 7C. Other example retention pin profiles include arectangular or complex cross section. The interface bores disclosedherein can be dimensioned to accept retention pins having differentdiameters or widths to set a predefined radial position of therespective seal arc segment relative to the engine longitudinal axis A.In other examples, a geometry of the interface bores differ from ageometry of the retention pins. For example, the retention pin 484 canbe utilized in one of the interface bores 274B/374B. As another example,the retention pin 284 can be utilized in one of the interface bores374B/474B.

FIG. 8 illustrates an assembly 560 according to another example. A firstretention feature 580 of a gas turbine engine component or seal arcsegment 566 is established by a first set of retention pins 584-1, and asecond retention feature 582 is established by a second set of retentionpins 584-2. The first set of retention pins 584-1 are received in afirst set of interface bores 574B-1 of first interface portion 574 toestablish a first installed position of the seal arc segment 566. Thesecond set of retention pins 584-2 are received in a second set ofinterface bores 574B-2 of the of first interface portion 574 toestablish a second installed position of the seal arc segment 566. Thefirst set of retention pins 584-1 are dimensioned to carry a load of theseal arc segment 566 in the first installed position. The second set ofretention pins 584-2 are dimensioned to carry a load of the seal arcsegment 566 in the second installed position, but not in the firstinstalled position.

The first set of interface bores 574B-1 are radially offset from thesecond set of interface bores 574-2. The second set of interface bores574-2 are dimensioned such that a radially outer surface 584RO of eachretention pin 584-2 is spaced apart from the respective interface bore574B-2 in the first installed position, but not the second installedposition of the seal arc segment 566.

FIG. 9 illustrates an assembly 660 according to yet another example. Aset of retention pins 684 are dimensioned to abut circumferentiallyopposed shoulders 675 of seal arc segment 666. The shoulders 675 canhave a generally dovetail geometry. The shoulders 675 can be utilized toestablish the first or second installed position of the seal arc segment666.

It should be understood that relative positional terms such as“forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like arewith reference to the normal operational attitude of the vehicle andshould not be considered otherwise limiting.

Although the different examples have the specific components shown inthe illustrations, embodiments of this disclosure are not limited tothose particular combinations. It is possible to use some of thecomponents or features from one of the examples in combination withfeatures or components from another one of the examples.

Although particular step sequences are shown, described, and claimed, itshould be understood that steps may be performed in any order, separatedor combined unless otherwise indicated and will still benefit from thepresent disclosure.

The foregoing description is exemplary rather than defined by thelimitations within. Various non-limiting embodiments are disclosedherein, however, one of ordinary skill in the art would recognize thatvarious modifications and variations in light of the above teachingswill fall within the scope of the appended claims. It is therefore to beunderstood that within the scope of the appended claims, the disclosuremay be practiced other than as specifically described. For that reasonthe appended claims should be studied to determine true scope andcontent.

What is claimed is:
 1. An assembly for a gas turbine engine comprising:a gas turbine engine component including a first interface portion; asupport including a mounting portion and a second interface portion, themounting portion attachable to an engine static structure; a firstretention feature that releasably secures the first interface portion tothe support in a first installed position of the gas turbine enginecomponent; and a second retention feature dimensioned to secure thefirst interface portion to the second interface portion in a secondinstalled position of the gas turbine engine component; and wherein thefirst installed position differs from the second installed position, andone of first and second retention features is dimensioned to carry thegas turbine engine component in response to release of another one ofthe first and second retention features.
 2. The assembly as recited inclaim 1, wherein the second retention feature includes an interfaceflange extending outwardly from the first interface portion and includesa support flange extending from the second interface portion, theinterface flange is dimensioned to sit on the support flange in thesecond installed position.
 3. The assembly as recited in claim 1,wherein the gas turbine engine component is a seal arc segment includinga sealing portion dimensioned to bound a gas path surface, the firstinterface portion includes an interface bore, the first retentionfeature includes a retention pin slidably received in the interface boreto secure the first interface portion to the support in the firstinstalled position of the seal arc segment, and the interface bore isdimensioned such that the seal arc segment sits on an outer periphery ofthe retention pin in the first installed position.
 4. The assembly asrecited in claim 3, wherein the second retention feature includes aninterface flange extending outwardly from the first interface portionand includes a support flange extending from the second interfaceportion, the interface flange is dimensioned to sit on the supportflange in the second installed position.
 5. The assembly as recited inclaim 4, wherein the second interface portion includes a support boredimensioned to at least partially receive the retention pin to establishthe first installed position of the seal arc segment.
 6. The assembly asrecited in claim 4, wherein the interface bore is dimensioned such thatthe seal arc segment sits on an outer periphery of the retention pin inthe first installed position.
 7. The assembly as recited in claim 6,wherein the interface flange of the seal arc segment comprises a ceramicmaterial.
 8. The assembly as recited in claim 7, wherein the interfaceflange includes a sacrificial member dimensioned to engage the supportflange in the second installed position.
 9. The assembly as recited inclaim 1, wherein the gas turbine engine component is a seal arc segmentincluding a sealing portion dimensioned to bound a gas path surface, andthe sealing portion and the first interface portion of the seal arcsegment comprise a ceramic material.
 10. The assembly as recited inclaim 1, wherein the gas turbine engine component is a seal arc segmentincluding a sealing portion dimensioned to bound a gas path surface, andfurther comprising a seal plate attachable to the support, and a sealmember captured between the seal arc segment and the seal plate, whereinthe first interface portion includes a first flange, the seal plateincludes a plate flange, and the plate flange is dimensioned to carrythe seal arc segment in the second installed position.
 11. The assemblyas recited in claim 10, wherein the first interface portion includes aninterface bore, the first retention feature includes a retention pinslidably received in the interface bore to secure the first interfaceportion to the support in the first installed position of the seal arcsegment, and the seal plate includes a plate bore dimensioned to atleast partially receive the retention pin to establish the firstinstalled position of the seal arc segment.
 12. A gas turbine enginecomprising: an engine case extending along an engine longitudinal axis;an array of blades rotatable about the engine longitudinal axis; and aseal assembly comprising: an array of blade outer air seals (BOAS)arranged about the array of blades, each of the BOAS including a sealingportion and a first interface portion, the sealing portion dimensionedto bound a core flow path, and the first interface portion including atleast one interface bore; at least one support attached to the enginecase; a first retention feature including a plurality of retention pinsdimensioned to engage the at least one support and the first interfaceportion of a respective one of the BOAS such that the BOAS are carriedby the retention pins in a first installed position; and a secondretention feature dimensioned to bound radial movement of the BOAStowards the engine longitudinal axis in a second installed position ofthe BOAS.
 13. The gas turbine engine as recited in claim 12, whereineach of the BOAS comprises a ceramic material.
 14. The gas turbineengine as recited in claim 12, wherein each of the retention pins isslidably received in a respective interface bore of the first interfaceportion and at least partially received in a respective support bore ofthe at least one support such that the first interface portion sits on aradially outer surface of the respective retention pin in the firstinstalled position.
 15. The gas turbine engine as recited in claim 14,wherein the seal assembly includes a seal plate releasably secured tothe at least one support, and each of the retention pins is insertedinto a respective plate bore of the seal plate to establish the firstinstalled position.
 16. The gas turbine engine as recited in claim 12,wherein a first retention hook of the first interface portion isdimensioned to sit on a second retention hook of the at least onesupport in the second installed position.
 17. A method of sealing for agas turbine engine comprising: positioning a first interface portion ofa seal arc segment relative to a second interface portion of a supportsuch that engagement of the first and second interface portionsestablishes a first installed position of the seal arc segment in whichthe seal arc segment is carried by the support; and inserting aretention pin in an interface bore of the seal arc segment and a supportbore of the support such that engagement of the retention pin withsurfaces of the interface bore and surfaces of the support boreestablishes a second installed position of the seal arc segment in whichthe seal arc segment is carried by the retention pin; and wherein one ofthe first and second installed positions is established in response torelease of the seal arc segment from another one of the first and secondinstalled positions subsequent to the positioning and inserting steps.18. The method as recited in claim 17, wherein the seal arc segmentcomprises a ceramic material.
 19. The method as recited in claim 17,further comprising securing a seal plate to the support, and insertingthe retention pin in a plate bore of the seal plate to establish thesecond installed position.
 20. The method as recited in claim 17,wherein the first interface portion includes a first flange, the secondinterface portion includes a second flange, and the first flange isdimensioned to sit on the second flange in the first installed position.